Color photographic elements are conventionally formed with superimposed blue, green, and red recording layer units coated on a support. The blue, green, and red recording layer units contain radiation-sensitive silver halide emulsions that form a latent image in response to blue, green, and red light, respectively. Additionally, the blue recording layer unit contains a yellow dye-forming coupler, the green recording layer unit contains a magenta dye-forming coupler, and the red recording layer unit contains a cyan dye-forming coupler.
Following imagewise exposure, a negative working photographic element is processed in a color developer that contains a color developing agent that is oxidized while selectively reducing to silver the latent image bearing silver halide grains. The oxidized color developing agent then reacts with the dye-forming coupler in the vicinity of the developed grains to produce an image dye. Yellow (blue-absorbing), magenta (green-absorbing) and cyan (red-absorbing) image dyes are formed in the blue, green, and red recording layer units, respectively. Subsequently the element is bleached (i.e., developed silver is converted back to silver halide) to eliminate neutral density attributable to developed silver and then fixed (i.e., silver halide is removed) to provide stability during subsequent room light handling.
When processing is conducted as noted above, negative dye images are produced. To produce corresponding positive dye images, and hence, to produce a visual approximation of the hues of the subject photographed, white light is typically passed through the color negative image to expose a second color photographic material having blue, green, and red recording layer units as described above, usually coated on a white reflective support. The second element is commonly referred to as a color print element. Processing of the color print element as described above produces a viewable positive image that approximates that of the subject originally photographed.
A positive working color photographic element is first developed in a black-and-white developer where the exposed crystals are selectively reduced to metallic silver. The unexposed silver is then fogged and reduced by a chromogenic color developer in a subsequent step to generate cyan, magenta, and yellow image dyes. The film is further bleached and fixed as with the negative working film. The positive working film thus forms dyes in the unexposed areas and renders a positive image of the scene, directly.
A problem with the accuracy of color reproduction delayed the commercial introduction of color negative elements. In color negative imaging, two dye image-forming coupler containing elements, a camera speed image capture and storage element and an image display, i.e. print element, are sequentially exposed and processed to arrive at a viewable positive image. Since the color negative element cascades its color errors forward to the color print element, the cumulative error in the final print is unacceptably large, absent some form of color correction. Even in color reversal materials which employ just one set of image dyes, color correction for the unwanted absorption of the imperfect image dyes is required to produce acceptable image color fidelity for direct viewing.
The complicated processing can be eliminated by substituting direct positive emulsions for the negative-working silver halide emulsions conventionally present in color reversal films. Unfortunately, direct positive emulsions are more difficult to manufacture, exhibit lower levels of sensitivity at comparable granularity, and have unique problems of their own, such as re-reversal, that have almost entirely foreclosed their use as replacements for negative-working emulsions.
Commercial acceptance of color negative elements occurred after commercial introduction of the first color reversal films. The commercial solution to the problem has been to place colored masking couplers in the color negative element. The colored masking couplers lose their color in areas in which grain development occurs, producing a dye image that is a reversal of the unwanted absorption of the image dye. This has the effect of neutralizing unwanted spectral absorption by the image dyes by raising the neutral density of the processed color negative element. However, this is not a practical difficulty, since this is easily offset by increasing exposure levels when exposing the print element through the color negative element.
In this regard, it should be noted that colored masking couplers have no applicability to reversal color elements. They actually increase visually objectionable dye absorption in a color negative film, superimposing an overall salmon colored tone, which can be tolerated only because color negative images are not intended to be viewed. On the other hand, color reversal images are made to be viewed, but not printed. Thus colored masking couplers, if incorporated in reversal films, would be visually objectionable and serve no useful purpose.
Radiation-sensitive silver halide grains possess native sensitivity to the near ultraviolet region of the spectrum, and high bromide silver halide grains possess significant levels of blue sensitivity. Blue recording layer units often rely on the native sensitivity of the high bromide silver halide emulsions they contain for light capture. Blue recording layer units sometimes and green and red recording layer units always employ spectral sensitizing dyes adsorbed to silver halide grain surfaces to absorb light and to transfer exposure energy to the radiation-sensitive silver halide grains. In a simple textbook model the light absorbed in each of the blue, green and red recording layer units is limited to just that one region of the spectrum. For blue, green and red recording layer units light absorption in the blue (400 to 500 nm), green (500 to 600 nm) and red (600 to 700 nm) spectral region, respectively, is sought with no significant absorption in any other region of the visible spectrum.
In practice each spectral sensitizing dye exhibits a peak (occasionally a dual peak) absorption wavelength and absorption declines progressively as exposure wavelengths diverge from the peak. Thus, considerable effort has gone into selecting spectral sensitizing dyes and dye combinations that best serve practical imaging needs, recognizing that uniform absorption over a 100 nm blue, green or red segment of the visible spectrum is impossible to realize, even when dye combinations are employed.
The use of spectrally sensitized tabular grain emulsions in the minus blue recording layer units of color photographic elements has been demonstrated by Kofron et al U.S. Pat. No. 4,439,520 to improve image sharpness and to increase speed in relation to granularity. Kofron et al demonstrates that improvements in performance are realized as the average aspect ratios of the tabular grain emulsions are increased.
Kofron et al further discloses a variety of layer arrangements for color photographic elements having blue, green and red recording layer units, including arrangements containing two or more of each of green and red recording layer units differing in speed. Other illustrations of color photographic elements containing two or more green and/or red recording layer units are provided by Research Disclosure, Vol. 389, September 1996, Item 38957, XI. Layers and layer arrangements.
Color correction means, for color negative or color reversal elements, have relied on imagewise interlayer development modification effects during wet chemical processing called interlayer interimage effects. In the case of color negative elements, these effects are most commonly achieved with development inhibitor releasing (DIR) couplers that imagewise release development inhibitors to reduce the extent of development of the receiving silver halide grains, and with colored masking couplers. In the case of color reversal elements, these effects are usually achieved through imagewise interlayer silver halide emulsion development inhibition during the first black-and-white development, and possibly with DIR couplers during the second color development step.
Alternatively, instead of optical print-through exposure to create a color print, the color negative or color reversal element can be scanned to record the blue, green, and red densities in each picture element (pixel) of the exposed area. The color correction that is normally achieved by chemical interlayer interimage effects can be achieved by electronically manipulating stored image information as its image-bearing signal. One example of electronic color correction produced by scanning a processed photographic recording material and manipulating the resultant image-bearing electronic signals to achieve improved color rendition can be found in the KODAK Photo CD.TM. Imaging Workstation system. In addition, optical printing by passing light through the processed photographic recording material to expose a second light-sensitive material is no longer necessary. The light exposures necessary to write the color-corrected output onto a suitable display material such as silver halide color paper exposed by red, green, and blue light emitting lasers can be calculated and those device-dependent writing instructions can be transmitted to such alternate printers as their code values (specific instructions for producing the correct color hue and image dye amount). Other means of electronic printing include thermal dye transfer material, color electrophotographic media, or a three color cathode ray tube monitor.
It has been found unexpectedly that different or larger color corrections can be managed by electronic color correction than can be achieved through chemical interlayer interimage effects in color negative or color reversal films. This enhanced capability allows the possibility of producing better colorimetric matches between the original scene color content and the rendered image reproduction. In order to accomplish improved color reproduction, more accurate photographic recording material spectral sensitivity is required. In particular, the spectral sensitivity of a film optimally designed for scanning and electronic color correction must more closely approach that of the human visual system. To accurately record colors the way the human eye perceives them, a recording element must have spectral sensitivities that are linear transformations of the blue, green, and red cone responses of the human eye. Such linear transformations are known as color matching functions. Color matching functions for any set of real primary stimuli must have negative portions. Within the realm of known photographic mechanisms, it is not possible to produce a photographic element having spectral sensitivities whose response is negative.
Examples of spectral sensitivities that approximate color matching functions are those of MacAdam (Pearson and Yule, J. Color Appearance, 2, 30 (1973). Giorgianni et al, U.S. Pat. No. 5,582,961 and U.S. Pat. No. 5,609,978, the disclosures of which are herein incorporated by reference, describe related spectral sensitivities applied to non-tabular emulsions in color reversal film elements capable of forming image representations that correspond more closely to the colorimetric values of the original scene upon scanning and electronic conversion. A characteristic of these color matching functions is a broad response for the green recording layer unit that has significant sensitivity at wavelengths between about 470 nm and 600 nm. This type of response function closely resembles the green response of the human eye and visual system.
The green sensitivity of a multilayer film element is determined by the light absorption profile of the silver halide emulsions in the green sensitive layer unit attenuated by any light absorbing materials that lie above it in the top layers of the film, such as ultraviolet filter dyes, Lippmann emulsions, yellow filter layers, the blue sensitive emulsions, the yellow and magenta colored masking couplers in color negative films, and the optical properties of the red sensitive emulsions underneath the green record. The light absorption of the emulsions used in the green sensitive layer unit is in turn determined by the composite absorption of the specific combination of spectral sensitizing dyes adsorbed to the surface of the silver halide crystals, since silver halide emulsions only have native (intrinsic) sensitivity to blue light. Green sensitive emulsions used in the green recording layer unit that are commonly found in the art are observed to employ two or three green sensitizing dyes, and they typically peak in dyed absorptance from about 530 nm to about 560 nm. Broad light absorptance to produce color reproduction accuracy in accord with human visual sensitivity was not sought.
Yamada et al in U.S. Pat. No. 5,376,508 employs a blend of two spectral sensitizing dyes to achieve a broad 80% absorption bandwidth, but with inadequate absorption in the short green region. Ikegawa et al in DE 3,740,340 A1 provides an example of a short green dye used alone which does not J-aggregate, which provides high absorption bandwidth and good absorption in the short green region, but very little sensitivity in the long green region, around 550nm and 560 nm. Another combination of two green dyes demonstrated in '340 also lacks sufficient absorption in the short green region. U.S. Pat. No. 5,460,928 Kam-Ng et al use a two dye combination for the green record, which again does not provide adequate short green absorption, and also provides inadequate half-peak bandwidth. Shiba et al in U.S. Pat. No. 5,037,728 demonstrate a three spectral sensitizing dyes with silver iodobromide emulsions with inadequate breadth at 80% of peak absorption and insufficient absorption at 520 nm. Sasaki in U.S. Pat. No. 5,053,324 demonstrates a short green spectral sensitizing dye combined with a long green spectral sensitizing dye which provides high absorption in the short green region and sufficient half-peak bandwidth, but a narrow breadth at 80% of peak absorption. Nozawa in U.S. Pat. No. 5,166,042 also presents three spectral sensitizing dye combinations which include a short green dye. Nozawa provides adequate sensitivity in the short green region, but narrow breadth at 80% of peak absorption and indequate sensitivity in the long green region at 550 nm. Sasaki et al in U.S. Pat. No. 5,077,182 again demonstrate two and three spectral sensitizing dye combinations which include a short green dye, providing broad half-peak bandwidth and adequate short green sensitivity, but low sensitivity in the long green 550 nm region. In U.S. Pat. No. 5,169,746 of Sasaki a three dye combination including a short green sensitizing dye is presented which provides good absorption in the long green region, but falls far short of the breadth required at 50% and 80% of peak absorption. Other three dye combinations presented lack the short green dye and these fail for short green absorption at 520 nm, as well as for breadth at 50% and 80% of peak absorption.
Ohashi et al in U.S. Pat. No. 4,599,301 use a two spectral sensitizing dye combination which provides high absorption breadth at 50% and 80% of peak absorption, but the maximum absorption of the emulsion falls at 564 nm, and the combination provides inadequate absorption in the short green region at 520 nm. Ezaki et al in U.S. Pat. No. 5,258,273 reveal the use of four spectral sensitizing dyes in combination; but the maximum absorption falls at 564 nm, with a half-peak bandwidth absorption of only 45 nm, and inadequate absorption in the short green region at 520 nm was achieved. Shimazaki et al in U.S. Pat. No. 5,206,124 and U.S. Pat. No. 5,206,126 use three dye combinations for the green record; and all provide a narrow half-peak bandwidth absorption and inadequate absorption in the short green region. U.S. Pat. No. 5,308,748 of Ikegawa et al provide examples of two, three, and four spectral sensitizing dye combinations. The two dye combinations are quite narrow for half-peak bandwidth. One three dye combination provides no significant absorption at 520 nm; the other three dye combination achieves adequate absorption at 520 nm, but a maximum absorption at 562 nm. The four dye combination is very narrow for half-peak bandwidth, provides inadequate absorption at 520 nm, and has a maximum absorption at 574 nm. Siegel et al in European Patent Application EP 0 866 368 A2 use up to three spectral sensitizing dyes concurrently with a silver iodobromide emulsion to achieve significant breadth in sensitivity at both 80% and 50% of the peak green sensitivity. However, no short green spectral sensitizing dye was used, and high sensitivity in the short green region is not achieved.
Schwan et al in U.S. Pat. No. 3,672,898 seek to produce multicolor photographic elements with acceptable neutrals and good color rendition under a variety of illuminants. However, Schwan et al specifically contemplate the use of a magenta-colored filter material which is used to trim green light from the red record. Giorgianni et al in U.S. Pat. No. 5,582,961 demonstrate a conventional, low aspect ratio silver iodobromide emulsion with three spectral sensitizing dyes; the inventive example provide inadequate breadth at both 50% and 80% of peak absorption and inadequate absorption at 520 nm. The comparative example which uses two dyes provides adequate half-peak bandwidth and absorption at 520 nm, but provides too narrow an absorption profile at 80% of peak absorption. Their goal of significantly broad green sensitivity which mimics the human visual system for improved color capture accuracy and reduced mixed illuminant sensitivity was not satisfied.